1. Field of the Invention
The present invention relates to siliceous crystalline compositions, a method for preparing same, and processes which involve its use. More particularly, the invention relates to siliceous crystalline compositions further containing a metallic component.
2. Prior Art
Silicon is second only to oxygen as the most prevalent element in the earth's crust (.about.28% by weight) and is found in widely diverse minerals. Free silica, for example, occurs in many crystalline forms, with quartz being by far the most prevalent form. Additionally, silicon chemically bonds with oxygen to form silicate minerals, and such minerals form the major constituents of the earth's outer layers. Silicates are also important constituents of meteorites and materials of lunar origin.
Among the commercially important silicate materials are the crystalline aluminosilicate zeolites, which occur in such natural forms as analcime, brewsterite, chabazite, clinoptilolite, dachiardite, erionite, faujasite, ferrierite, gismondine, gmelinite, heulandite, laumontile, levynite, mesolite, mordenite, natrolite, offretite, phillipsite, paulingite, scolecite, stilbite, and thomsonite. The commercial usefulness of zeolites encouraged the rapid development of synthetic zeolites, and a great number are now known, the following being among those disclosed in the patent literature: Zeolite A (U.S. Pat. No. 2,882,243), Zeolite B (U.S. Pat. No. 3,008,803), Zeolite D (Canadian Pat. No. 661,981), Zeolite E (U.S. Pat. No. 2,962,355), Zeolite F (U.S. Pat. No. 2,996,358), Zeolite H (U.S. Pat. No. 3,010,789), Zeolite J (U.S. Pat. No. 3,011,869), Zeolite L (U.S. Pat. No. 3,216,789), Zeolite M (U.S. Pat. No. 2,995,423), Zeolite O (U.S. Pat. No. 3,140,252), Zeolite Q (U.S. Pat. No. 2,991,151), Zeolite R (U.S. Pat. No. 3,030181), Zeolite S (U.S. Pat. No. 3,054,657), Zeolite T (U.S. Pat. No. 2,950,952), Zeolite W (U.S. Pat. No. 3,012,853), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite Z (U.S. Pat. No. 2,972,516), Zeolite ZSM-4 (Canadian Pat. No. 817,915), and Zeolite Beta (U.S. Pat. No. 3,308,069). Other zeolites are also known, as for example, Zeolite Z-14US disclosed in U.S. Pat. No. 3,293,192, the zeolites disclosed in U.S. Pat. No. 3,227,660, and Zeolite ZSM-2 (U.S. Pat. No. 3,411,874), Zeolite Z-14 (U.S. Pat. No. 3,619,134), Zeolite K-G (U.S. Pat. No. 3,056,654), Zeolite ZK-4 (U.S. Pat. No. 3,314,752), Zeolite ZK-5 (U.S. Pat. No. 3,247,195), Zeolite ZK-21 (U.S. Pat. No. 3,355,246), Zeolite UJ (U.S. Pat. No. 3,298,780), and Zeolite W-Z (U.S. Pat. No. 3,649,178).
Both the natural and synthetic zeolites are comprised of a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 tetrahedra joined by crosslinking oxygen atoms, and the resulting crystal lattice has an electronegative charge balanced by the inclusion of cations, sodium being almost exclusively found as the cation. The cations have considerable freedom of movement within the crystal framework and may be removed by ion exchange.
Because of their great affinity for adsorbing water, one of the first uses of zeolites was for drying or desiccation purposes. But other uses soon developed. In particular, due to their unique crystal structure, wherein each form of zeolite contains pore openings or cavities of microscopic size, many zeolites have been used as molecular sieves, that it, as agents for separating one molecule from another based upon the size of a molecule or portion thereof. Additionally, certain zeolites have been found to have catalytic properties with respect to hydrocarbon conversion reactions, as for example, in the cracking of hydrocarbons. These catalytic properties depend at least in part upon the zeolite having pore openings of sufficient size to allow ingress of relatively large hydrocarbon molecules into the interior of the crystal structure. Also critical is the presence of acid sites within the zeolite, which acid sites are usually produced by replacing some or all of the metal cations within the zeolite with hydrogen ions, using procedures well known in the art.
One zeolite of enormous importance in the catalysis of hydrocarbon conversion reactions is Zeolite Y, a zeolite having pores of diameter between about 6 and 15 angstroms, large enough to permit entry of even relatively large aromatic molecules into the zeolite. Zeolite Y, as disclosed in U.S. Pat. No. 3,130,007, has an X-ray powder diffraction pattern as shown in the following Table I, which reports all lines of at least weak intensity:
TABLE I ______________________________________ Interplanar spacing d(A) Relative Intensity ______________________________________ 14.37-14.15 VS 8.80-8.67 M 7.50-7.39 M 5.71-5.62 S 4.79-4.72 M 4.46-4.33 M 4.29-4.16 W 4.13-4.09 W 3.93-3.88 W 3.79-3.74 S 3.66-3.62 M 3.33-3.28 S 3.04-3.00 M 2.93-2.89 M 2.87-2.83 S 2.78-2.74 M 2.73-2.69 W 2.65-2.61 M 2.39-2.36 M 2.20-2.17 W 2.11-2.08 W 1.76-1.73 W 1.71-1.69 W ______________________________________
Zeolites of the Y type are of especial usefulness in the cracking or hydrocracking of hydrocarbons, particularly when ion-exchanged to contain hydrogen ions and when stabilized by either a partial ion exchange with rare earth cations as disclosed in U.S. Pat. Nos. 3,140,253 and 3,210,267 or by a steam calcination treatment as disclosed in U.S. Pat. No. 4,036,739.
Recently, another crystalline aluminosilicate zeolite, designated ZSM-5, has been established as useful in hydrocarbon conversion catalysis. ZSM-5 is particularly useful in the art of catalytic dewaxing because its uniform pore openings of between about 5 and 6 angstroms are especially suited to admitting waxy paraffinic hydrocarbons while rejecting larger-sized molecules. ZSM-5 zeolite is more particularly described in U.S. Pat. No. 3,702,886 wherein the following X-ray powder diffraction pattern is set forth:
TABLE II ______________________________________ Interplanar spacing d(A): Relative intensity ______________________________________ 11.1 .+-. 0.2 S 10.0 .+-. 0.2 S 7.4 .+-. 0.15 W 7.1 .+-. 0.15 W 6.3 .+-. 0.1 W 6.04 .+-. 0.1 W 5.97 5.56 .+-. 0.1 W 5.01 .+-. 0.1 W 4.60 .+-. 0.08 W 4.25 .+-. 0.08 W 3.85 .+-. 0.07 VS 3.71 .+-. 0.05 S 3.04 .+-. 0.05 W 2.99 .+-. 0.02 W 2.94 .+-. 0.02 W ______________________________________
The commercial interest in ZSM-5 zeolite led to the development of a large number of zeolites similar to ZSM-5, which zeolites are exemplified by ZSM-8 (U.S. Pat. No. 3,700,585), ZSM-11 (U.S. Pat. No. 3,709,979), ZSM-12 (U.S. Pat. No. 3,832,449), ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-23 (U.S. Pat. No. 4,076,842), ZSM-25 (U.S. Pat. No. 4,247,416), ZSM-35 (U.S. Pat. No. 4,016,245), ZSM-39 (U.S. Pat. No. 4,259,306). Also known are certain ferrierite-type zeolites known as ZSM-21 and ZSM-38 (U.S. Pat. No. 4,046,859) as well as other zeolites such as ZSM-18 (U.S. Pat. No. 3,950,496) and ZSM-43 (U.S. Pat. No. 4,209,497).
In addition to the crystalline aluminosilicate zeolites, certain siliceous crystalline materials consisting essentially of silica polymorphs are also useful as molecular sieves. One such silica polymorph is termed "silicalite" and is described more thoroughly in U.S. Pat. No. 4,061,724. Although similar to ZSM-5 in many respects, silicalite differs in that it is essentially free of aluminum and, unlike the zeolites, is hydrophobic and exhibits essentially no ion exchange properties. Silicalite is further characterized by a crystal structure comprising a channel system (or pore structure) of straight channels having an elliptical cross-section, which straight channels are intersected perpendicularly by zigzag channels of nearly circular cross-section. (See "Silicalite, a New Hydrophobic Crystalline Silica Molecular Sieve" by Flanigen et al., published in Nature, Volume 271, pp. 512 to 516, Feb. 9, 1978.) As reported in U.S. Pat. No. 4,061,724, the X-ray powder diffraction pattern of silicalite shows the following lines having a relative intensity of at least 10 percent of the intensity of the strongest line:
TABLE III ______________________________________ Interplanar Relative Spacing Intensity d(Angstroms) I/I.sub.o ______________________________________ 11.1 100 10.02 64 9.73 16 5.98 14 3.85 59 3.82 32 3.74 24 3.71 27 3.64 12 3.34 11 2.98 10 ______________________________________
Besides zeolites and silica polymorphs, other siliceous crystalline materials are known in the art, and these include the synthetic organosilicates disclosed in U.S. Pat. No. 4,104,294, the silicates disclosed in U.S. Pat. No. 4,208,305, and the metal organosilicates disclosed in U.S. Pat. No. Re. 29,948. In view of these patents, and the numerous patents relating to zeolites, and the published literature relating to silicalite (and similar materials such as "Silicalite-2," a composition disclosed in an article entitled "Silicalite-2, a Silica Analogue of the Aluminosilicate Zeolite ZSM-11," published in Nature by Bibby et al., Volume 280, pages 664 and 665, Aug. 23, 1979), it is evident that there is an ongoing effort in the art to develop new and useful siliceous crystalline materials, especially those having a uniform pore structure.
The main object of the invention is to provide a metal-containing siliceous crystalline material useful in catalysis, as for example in the hydrodewaxing of paraffinic hydrocarbons. Another object is to provide a method for synthesizing metal-containing siliceous crystalline materials, and especially rare earth, siliceous crystalline materials. Yet another object is to provide a catalytic process wherein the crystalline composition of the invention is utilized as a catalyst or component thereof. These and other objects and advantages will reveal themselves to those skilled in the art in light of the following description of the invention.